All this talk of light pressure gives me gas.

If we have neutral atoms / molecules in intergalactic space, won't
light pressure tend to brake them to average neutral speed wrt the
Universe at large?

They aren't terribly massive, so the (for example) temperature
difference between the "poles" of the CMBR that we experience, should
brake them in finite time.

Note sure where I am going with this, other than it will make capture
by nearby bodies easier, or coalescence into new galaxies possible.
http://arxiv.org/abs/1006.2166

David A. Smith

dlzc wrote in news:41071260-d62b-4903-b2be-
:

If we have neutral atoms / molecules in intergalactic space, won't
light pressure tend to brake them to average neutral speed wrt the
Universe at large?

They aren't terribly massive, so the (for example) temperature
difference between the "poles" of the CMBR that we experience, should
brake them in finite time.

The CMB dipole is only there becauase we are moving with respect to the
dipole=0 frame.


Note sure where I am going with this, other than it will make capture
by nearby bodies easier, or coalescence into new galaxies possible.
http://arxiv.org/abs/1006.2166

David A. Smith

"dlzc" wrote in message
...
| If we have neutral atoms / molecules in intergalactic space, won't
| light pressure tend to brake them to average neutral speed wrt the
| Universe at large?
|
| They aren't terribly massive, so the (for example) temperature
| difference between the "poles" of the CMBR that we experience, should
| brake them in finite time.
|
| Note sure where I am going with this, other than it will make capture
| by nearby bodies easier, or coalescence into new galaxies possible.
| http://arxiv.org/abs/1006.2166
|
| David A. Smith
|
What does a tsunami do to a fishing float?
http://wwwdelivery.superstock.com/WI...1779R-2611.jpg

Dear eric gisse:

On Nov 1, 7:57*pm, eric gisse wrote:
wrote in news:41071260-d62b-4903-b2be-
:

If we have neutral atoms / molecules in intergalactic space, won't
light pressure tend to brake them to average neutral speed wrt the
Universe at large?

They aren't terribly massive, so the (for example) temperature
difference between the "poles" of the CMBR that we experience,
should brake them in finite time.

The CMB dipole is only there because we are moving with respect
to the dipole=0 frame.

Agreed. Which means any given "cubic mile" of neutral gas, should be
non-moving wrt the CMBR frame (which is more or less the same frame as
the surveyed galaxies). How far outside the nearest galaxy that would
have to be, remains to be seen.

Note sure where I am going with this, other than it will make
capture by nearby bodies easier, or coalescence into new
galaxies possible.
http://arxiv.org/abs/1006.2166

So should the heliosheath be encountering neutral gas at ~300 km/sec
(or a bit more with gravitation)?

David A. Smith

dlzc wrote in news:02f47c8c-9093-46e2-a6d7-
:

[...]

So should the heliosheath be encountering neutral gas at ~300 km/sec
(or a bit more with gravitation)?

David A. Smith


Significantly less. The gas around the sun is largely immobile with respect
to the sun because are all sharing roughly the same orbit around the
galaxy.

Dear eric gisse:

On Nov 2, 3:01*pm, eric gisse wrote:
dlzc wrote in news:02f47c8c-9093-46e2-a6d7-
:

[...]

So should the heliosheath be encountering neutral gas at
~300 km/sec (or a bit more with gravitation)?

Significantly less. The gas around the sun is largely immobile
with respect *to the sun because are all sharing roughly the
same orbit around the galaxy.

I am sorry I used the wrong word. I meant heliopause, the surface of
highest "pressure" where the interstellar (only?) and solar gas
streams meet.
http://arxiv.org/abs/0707.2970

David A. Smith

In article ,
dlzc writes:
If we have neutral atoms / molecules in intergalactic space, won't
light pressure tend to brake them to average neutral speed wrt the
Universe at large?

Yes, but the effect today is tiny. How much light pressure does a
2.7 K source exert? The effect was significant, though, prior to
recombination. You might want to do a web search on "baryon acoustic
oscillations."

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On 01/11/2011 8:23 PM, dlzc wrote:
If we have neutral atoms / molecules in intergalactic space, won't
light pressure tend to brake them to average neutral speed wrt the
Universe at large?

Neutral gas is too diffuse to be braked by light pressure. Macroscopic
objects that are dense balls of gas or liquid, or solid be the only
things affected by light pressure.

They aren't terribly massive, so the (for example) temperature
difference between the "poles" of the CMBR that we experience, should
brake them in finite time.

Note sure where I am going with this, other than it will make capture
by nearby bodies easier, or coalescence into new galaxies possible.
http://arxiv.org/abs/1006.2166

So what exactly do you see in this paper about Luminous Infrared
Galaxies that you think is relevant to light pressure?

Yousuf Khan

Dear Yousuf Khan:

On Nov 3, 11:39*pm, Yousuf Khan wrote:
On 01/11/2011 8:23 PM,dlzcwrote:

If we have neutral atoms / molecules in intergalactic space,
won't light pressure tend to brake them to average neutral
speed wrt the Universe at large?

Neutral gas is too diffuse to be braked by light pressure.

Diffuse neutral gas has the same laws of physics as non-diffuse, at
least until a Bose-Einstein state is set up. As a discrete diffuse
gas, it will suffer "friction" with the CMBR, since most molecules
interact with microwaves.

Macroscopic objects that are dense balls of gas or liquid,
or solid be the only things affected by light pressure.

Why? Light is discrete, as are the bits "objects" are made of. Even
LeSage gravitation (which light could be the actor for, in some sense)
works on both the large and the small. Or do you imagine the universe
around smaller objects is not expanded, while for larger it is?

I am not trying to make fun of your (current favorite) idea here. I
am following a parallel path is all. This thread isn't about
"expansion", but about a possible "preferred background" established
by the CMBR itself. And if the "preferred background is detectable in
some way, can be validated by heliopause and stellarpause (maybe even
"galacticpause") measurements, then we can find out how much neutral
gas there is on average. I really don't think there is much, or we
could not see as far as we do. Also, if it were present, I think it
would tend to strip other neutral gas from passing galaxies...

They aren't terribly massive, so the (for example) temperature
difference between the "poles" of the CMBR that we
experience, should brake them in finite time.

Note sure where I am going with this, other than it will make
capture by nearby bodies easier, or coalescence into new
galaxies possible.
http://arxiv.org/abs/1006.2166

So what exactly do you see in this paper about Luminous
Infrared Galaxies that you think is relevant to light pressure?

Gas that doesn't move significantly, that may not be entirely
uniformly distributed, would be free to form luminous structures later
in the Universe's history. Brightness then would be expected to
increase with time, as the structure loses energy, and falls into even
tighter arrangements.

Not saying the above paper even talks about good candidates for this.
I am reminded of a really cool (as in not very bright, infrared)
galaxy we had completely overlooked, right in our neighborhood, that
was announced a few years ago, but didn't try really hard.

David A. Smith

Dear Steve Willner:

On Nov 3, 3:02*pm, (Steve Willner) wrote:
In article ,

*dlzc writes:
If we have neutral atoms / molecules in intergalactic space,
won't light pressure tend to brake them to average neutral
speed wrt the Universe at large?

Yes, but the effect today is tiny. How much light pressure
does a 2.7 K source exert?

This particular source is hundreds of watts per square meter, since it
is a whole sky source.

*The effect was significant, though, prior to recombination.
*You might want to do a web search on "baryon acoustic
oscillations."

Thanks.

David A. Smith